The only way (at least that I know of) to change color is to split
your data and do several scatterplots:
twoway (scatter ... if z>=9, ... mcolor(gs12)) (scatter ... if z>7.5 &
z<9, ... mcolor(gs8)) (scatter ... if z<7.5, ... mcolor(gs4))
This can probably be automated with a ~15 line wrapper program that
takes in z, y, z and the thresholds.
Graphics in R is notably stronger than in Stata.
On Sun, Aug 24, 2008 at 10:42 AM, David Airey
<david.airey@vanderbilt.edu> wrote:

.

At this page, we see how to change symbol size by using (analytic)
weights: